This NPC stuck their shield up in front of them and refused to fight (hey, she started it ) - when I moved round to the side, she kept the shield up in front of her but only turned her head - she made no actual effort to defend herself or do anything different while I slowly shot arrows into her. I was able to stop and take breaks (and take a screenshot). Her shield protected her from the front, but once I was round to the side it seemed to offer no protection, and her failure to turn meant that she was just a static target.
Seems probably related to the old bug of NPCs putting their shield up and refusing to stop blocking - I think that was another one that was fixed not long ago, which just adds to my suspicion that this patch is built on the wrong game version.